1. Field of the Invention
The present invention relates to a method for forming a spherical concave surface for supporting a body with a spherical convex surface, and, more specifically, to a method for forming a spherical concave surface suitable for supporting a shoe with a spherical convex surface at an end portion of a piston in an inclined plate-type compressor.
2. Description of Related Art
In a known inclined plate-type compressor, generally a pair of shoes each having a spherical convex surface engage an end portion of a piston. The rotational movement of an inclined plate rotated by a drive shaft is converted into the reciprocal movement of the piston via the engagement of the shoes with the end portion of the piston and the radial outer surface of the inclined plate. The piston compresses fluid by its reciprocal movement. Each shoe may have a flat surface engaging the radial outer side surface of the inclined plate, and a spherical convex surface engaging and supported by a spherical concave surface formed at the end portion of the piston.
FIG. 3 depicts a known inclined plate-type compressor. Each piston 1 is reciprocally inserted into corresponding cylinder bore 2 formed in cylinder block 3. Crank chamber 4 is formed by cylinder block 3 and front housing 5. Drive shaft 6 extends through crank chamber 4, and is rotatably supported by cylinder block 3 and front housing 5. Inclined plate 7 rotates integrally with drive shaft 6 via rotor 8 and may form a variable inclined plate angle with drive shaft 6. The radial outer portion of inclined plate 7 runs through groove 11 formed at the end portion of piston 1, when inclined plate 7 rotates. A pair of shoes 9 are provided at the end portion of piston 1. Each shoe 9 has flat surface 9a slidably engaging the radial outer side surface of inclined plate 7, and spherical convex surface 9b slidably engaging and supported by a pair of spherical concave surfaces 1a and 1b formed at the end portion of piston 1. The rotational movement of inclined plate 7 is converted into the reciprocal movement of each piston 1 via the pair of shoes 9.
FIG. 4 depicts a known method for forming spherical concave surfaces 1a and 1b at the end portion of piston 1. Groove 11, through which the radial outer portion of inclined plate 7 passes, is provided at the end portion of piston 1. Cutting edge 14 of tool 12 (a cutting tool) is brought into contact with an inner side surface of groove 11. At that time, central axis L2 of supporting base 13 of tool 12 is set parallel to central axis L1 of groove 11. With tool 12 and piston 1 in this relative orientation, and while piston 1 is rotated around central axis L1 of groove 11, tool 12 is moved concordantly in first direction Y parallel to axis L2 of supporting base 13 of tool 12 and in second directions X1 and X2 perpendicular to first direction Y. During this method, cutting edge 14 of tool 12 moves along an arced path, so that it moves from point P1 to point P3 through point P2. In such a manner, spherical concave surfaces 1a and 1b are formed about central axis L1 of groove 11.
In the above-described known forming method, however, when cutting edge 14 passes through point P2, the moving direction of supporting base 13 changes from direction X2 to direction X1. Namely, when cutting edge 14 is moved along the arced form of spherical concave surface 1a, although supporting base 13 is moved in direction X2 as cutting edge 14 forms a portion between points P1 and P2, supporting base 13 is moved in direction X1 as cutting edge 14 forms a portion between points P2 and P3.
Consequently, a sudden recoil may occur in a power transmitting mechanism of a controlling machine (not shown) for moving supporting base 13 when the direction of movement changes from direction X2 to direction X1 at point P2. The generation of such a sudden recoil may not achieve a proper movement of cutting edge 14, and spherical concave surfaces 1a and 1b may not be formed in the desired target shapes.
Accordingly, it is an object of the present invention to provide an improved method for formig a spherical concave surface in a desired shape without generating a sudden recoil in a controlling machine.
It is another object of the present invention to provide an improved method for forming a spherical concave surface suitable for supporting a shoe with a spherical convex surface at an end portion of a piston in an inclined plate-type compressor.
To achieve the foregoing and other objects, a method for forming a spherical concave surface according to the present invention is herein provided. The method for forming a spherical concave surface comprises the steps of bringing a tool into contact with a material to be formed, rotating the material around a predetermined axis, and moving the tool in a first direction parallel to a central axis of the tool and in a second direction perpendicular to the first direction for forming the spherical concave surface on the material about the predetermined axis. In this method, a first angle of the central axis of the tool relative to the predetermined axis is selected to be greater than or equal to, i.e., not less than, a second angle of a tangent at a first end of the spherical concave surface in a cross-sectional plane including the predetermined axis relative to the predetermined axis.
Further, the present invention provides a method for forming a spherical concave surface on an end portion of a piston of an inclined plate-type compressor. The method comprises the steps of: providing a groove on the end portion of the piston, in which groove the depth direction extends along a predetermined axis; bringing a tool into contact with an inner side surface of the groove; rotating the piston around the predetermined axis; and moving the tool in a first direction parallel to a central axis of the tool and in a second direction perpendicular to the first direction for forming the spherical concave surface on the inner side surface of the groove about the predetermined axis. The groove is adapted to receive a radial outer portion of a rotating inclined plate. In this method, a first angle of the central axis of the tool relative to the predetermined axis is selected to be greater than or equal to, i.e., not less than, a second angle of a tangent at a first end of the spherical concave surface in a cross-sectional plane including the predetermined axis relative to the predetermined axis.
In the method, the tool is moved in a single direction along the second direction while the tool is moved in a single direction along the first direction.
In the method according to the present invention, because the first angle is greater than or equal to, i.e., not less than, the second angle, the tool may be moved only in one direction, that is the second direction, when the spherical concave surface is formed. Because the moving direction of the tool does not change, a sudden recoil does not occur when the tool is moved by a power transmitting mechanism of a forming machine. A cutting edge of the tool may be moved along a properly arced route along a spherical concave surface to be formed, without any undesirable variation. Consequently, the spherical concave surface may be accurately formed in a desired target shape.
Further objects, features, and advantages of the present invention will be understood from the following detailed description of preferred embodiments of the present invention with reference to the accompanying figures.